Block copolymers that include a poly(phenylene ether) block and a polysiloxane block are known materials that are useful components of various thermoplastic and thermoset compositions. Their polysiloxane content makes them particularly useful as flame retardant additives. They can also be employed as compatibilizers to stabilize otherwise poorly compatible blends of polysiloxanes with aromatic polymers, such as polystyrenes, poly(phenylene ether)s, aromatic polyesters, aromatic polyamides, and aromatic polyimides.
Poly(phenylene ether)-polysiloxane block copolymers are most efficiently prepared by oxidative copolymerization of a monohydric phenol and a hydroxyaryl-terminated polysiloxane. For example, Banach et al. in U.S. Pat. No. 5,357,022 have reported the oxidative copolymerization of 2,6-dimethylphenol and a silicone macromer having terminal phenol groups. And Carrillo et al. in U.S. Patent Application Publication No. 2009/0318635 A1 describe an improved method of oxidative copolymerization that increases the extent of silicone macromer incorporation into the block copolymer.
One disadvantage of known poly(phenylene ether)-polysiloxane block copolymers is that they have a lower glass transition temperature than the corresponding poly(phenylene ether). This means that although the substitution of poly(phenylene ether)-polysiloxane block copolymer for poly(phenylene ether) may increase the flame retardancy of a polymer blend, it can also decrease the heat resistance of the blend. There is therefore a need for poly(phenylene ether)-polysiloxane block copolymers that provide improved heat resistance.